Modular Supramolecular Approach for Co-Crystallization of Donors and Acceptors into Ordered Networks

ABSTRACT

Organic charge-transfer (CT) co-crystals in a mixed stack system are disclosed, wherein a donor molecule (D) and an acceptor molecule (A) occupy alternating positions (DADADA) along the CT axis. A platform is provided which amplifies the molecular recognition of donors and acceptors and produces co-crystals at ambient conditions, wherein the platform comprises (i) a molecular design of the first constituent (α-complement), (ii) a molecular design of the second compound (β-complement), and (iii) a solvent system that promotes co-crystallization.

This application is a continuation of and claims priority to and thebenefit of application Ser. No. 13/476,974 filed May 21, 2012, whichclaimed priority to and the benefit of application Ser. No. 61/488,605filed May 20, 2011 and application Ser. No. 61/498,277 filed on Jun. 17,2011—each of which is incorporated herein by reference in its entirety.

This invention was made with government support under DE-SC0000989awarded by the Department of Energy and DMR0520513 awarded by theNational Science Foundation. The government has certain rights in theinvention.

FIELD OF THE INVENTION

The present invention relates generally to supramolecular chargetransfer networks that exhibit ferroelectric polarization switching witha ferroelectric Curie temperature above room temperature. The polar andswitchable systems disclosed herein utilize a synergy between hydrogenbonded networks and charge transfer complexation of donors and acceptormolecules in the mixed stack. This supramolecular motif is a startingpoint for the development of other functional organic systems that canswitch under the influence of electric fields at practical temperatures.

BACKGROUND OF THE INVENTION

Since the middle of the 20th Century, organic co-crystals have been ofinterest to a number of researchers. Saunder, D. H. Proc. R. Soc.London, Ser. A 1946, 188, 31-51; Vanniekerk, J. N., et al. ActaCrystallogr. 1948, 1, 44-44; Andrews, L. J. Chon. Rev. 1954, 54,713-776; McConnell, H. J. Chem. Phys. 1954, 22, 760-761; McConnell, H.M., et al. Proc. Natl. Acad. Sci. U.S.A. 1965, 53, 46-50; and Desantis,F., et al. Nature 1961, 191, 900-901. Charge-transfer (CT) co-crystals,in particular, have been studied for their structural modularity andnovel properties. Herbstein, F. H. Crystalline Molecular Complexes andCompounds: Structures and Principles, Oxford University Press: Oxford,N.Y., 2005; Klosterman, J. K., et al. Chem. Soc. Rev. 2009, 38,1714-1725; Jerome, D., et al. Adv. Phys. 2002, 51, 293-479; Horiuchi,S., et al. J. Phys. Soc. Jpn. 2006, 75, 051016; Saito, G., et al. Bull.Chem. Soc. Jpn. 2007, 80, 1-137. They are modular, inexpensive, andsolution-processable materials that can be designed to exhibitproperties such as ferroelectricity, conductance, magnetism, and opticalnonlinearity. Although the properties of these crystals are wellunderstood, there has been very little research aimed at incorporatingthem into organic electronic devices.

The lattice is composed of an electron deficient molecule, the acceptor(A), and an electron-rich constituent, the donor (D). When the donor andacceptor are complexed, an electron wave oscillates between them, i.e.,the CT. In the most basic model, the CT interaction can be viewed as acharge donation from the donor HOMO to the acceptor LUMO. Torrance, J.B., et al. Phys. Rev. Lett. 1981, 46, 253-257. More comprehensiveresearch on the ground state of DA co-crystals reveals, however, thatthe CT interaction actually varies significantly in terms of itsstructure and complexity. Murata, T., et al. J. Am. Chem. Soc. 2007,129, 10837-10846; Saito, G., et al. Philos. Trans. R. Soc. London, Ser.A 2008, 366, 139-150. For convenience, CT is typically categorized bythe parameter ionicity (p) that represents the degree of electrondonation (0≦p≦1) between the donor and the acceptor

$\left( {{D\overset{e -}{}A} = {D^{+ P}A^{- P}}} \right).$

Electron donor-acceptor ordered networks are good candidates for organicferroelectrics because of the possible long range orientation of chargetransfer dipoles. The canonical electron donor-acceptor (DA) systems,the mixed stack tetrathiafulvalene (TTF) with halogenated quinones, likeTTF-chloranil (TTF·QCl₄) and TTF-bromanil (TTF·QBr₄), have beeninvestigated by X-ray crystallography, vibrational spectroscopy, andelectrical measurements. Horiuchi, S., et al. Science 2003, 299, 229-232(2003); Horiuchi, S., et al. Nature Mater. 7, 357-366 (2008); Collet, E.et al. Science 300, 612-615 (2003); Kagawa, F., et al. Nat Phys 6,169-172 (2010); Torrance, J. B. et al. Phys. Rev. Lett. 47, 1747-1750(1981); Girlando, A., et al. J. Chem. Phys. 79, 1075-1085 (1983);Okamoto, H. et al. Phys. Rev. B 43, 8224-8232 (1991); Soos, Z. G. Chem.Phys. Lett. 440, 87-91 (2007); and Kagawa, F. et al. Phys. Rev. Lett.104, 227602-227606 (2010). The TTF·QCl₄ complex undergoes aferroelectric phase transition, associated with a discontinuous jump inionicity (p) at the Curie temperature (T_(c)=81 K), and dimerizationinto DA pairs (D⁰ A⁰ D⁰ A⁰ □D^(δ+)A^(δ−) D^(δ+)A^(δ−)) breakingcentro-symmetry. Categorizing this critical point as a ferroelectrictransition was first postulated in 1991 when an anomalous dielectricspike was also observed at T, for TTF·QCl₄. The TTF·QBr₄ crystal,already ionic (ρ>0.5) at room temperature, also dimerises into DA pairsat 53° K as result of a spin-Peierls instability. Girlando, A., et al.Solid State Commun. 54, 753-759 (1985). Even with a ferroelectric groundstate, however, measuring reversible polarization under an electricfield has only been shown in TTF·QBr₄.

Conventional organic CT crystals can be co-crystallized into twodifferent packing arrangements, segregated stacks and mixed stacks.Anderson, P. W., et al. Solid State Commun. 1973, 13, 595-598; Iwasa,Y., et al. Phys. Rev. B: Condens. Matter 1990, 42, 2374-2377;Kuwatagonokami, M., et al. Nature 1994, 367, 47-48; and Hamilton, D. G.,et al. Aust. J. Chem. 1997, 50, 439-445. In segregated stacks, the donorand acceptor pack edge-to-edge in separate columns (DDD, AAA), while incrystals with a mixed stack motif, the donor and acceptor occupyalternating positions (DADADA) along the CT axis. These two packingarrangements have considerably different physical properties.Co-crystals with segregated stacks typically exhibit metallicconductivity since the overlapping n orbitals between stacks of openshell donors and acceptors merge into conduction bands. Jerome, D. Chem.Rev. 2004, 104, 5565-5591. A mixed stack system is primarily known forpolar phase transitions with changes in temperature, variations inpressure and optical excitation. Bruinsma, R., et al. Phys. Rev. B:Condens. Matter 1983, 27, 456-466; Masino, M., et al. Phys. Chern.Chern. Phys. 2001, 3, 1904-1910; Iwasa, Y., et al. Synth. Met. 1991, 42,1827-1830; Tokura, Y., et al. Solid State Cornmun. 1986, 57, 607-610;Girlando, A., et al. Solid State Commun. 1986, 57, 891-896; andKoshihara, S., et al. Phys. Rev. B: Condens. Matter, 1990, 42,6853-6856. Other exotic physical phenomena, like nonlinear electronictransport, magnetic ordering, and optical nonlinearity, have beenidentified in mixed stack crystals as well. Ferraris, L., et al. J Am.Chern. Soc. 1973, 95, 948-949; Samoc, M., et al. J. Chem. Phys. 1983,78, 1924-1930; Massa, D., et al. Mol. Cryst. Liq. Cryst. Sci. 1989, 175,93-117; Kondo, R., et al. Chem. Lett. 1999, 333-334; Kondo, R., et al.Synth. Met. 2001, 120, 995-996; Mitani, T, et al. Phys. Rev. Lett. 1984,53, 842-845; Tokura, Y, et al. Phys. Rev. B: Condens. Matter 1988, 38,2215-2218; Iwasa, Y, et al. Phys. Rev. B: Condens. Matter 1989, 39,10441-10444; Hughes, R C., et al. J Chem. Phys. 1968, 48, 1066-1076;Huizinga, S., et al. Phys. Rev. B: Condens. Matter 1979, 19, 4723-4732;Hasegawa, T, et al. Solid State Commun. 1997, 103, 489-493; Kagawa, F.,et al. Nature Phys. 2010, 6, 169-172; Rao, S. M., et al. J Appl. Phys.1991, 70, 6674-6678; Ezaki, H., et al. Solid State Commun. 1993, 88,211-216; Mazumdar, S., et al. Chern. Phys. 1996, 104, 9283-9291; Wong,M. S., et al. Adv. Mater. 1997, 9, 554-557; Zyss, J., et al. Chern.Mater. 2003, 15, 3063-3073.

Research that relies on organic co-crystals presents numerouschallenges. Most notably, it can be difficult to grow high qualitycrystals that are large enough for experiments in integrated systems anddevices. Being able to produce these materials quickly and reproduciblywould facilitate their use in basic research and also in applications.It is therefore desirable to provide a self-assembly platform whichamplifies the molecular recognition of donors and acceptors and producesco-crystals at ambient conditions.

SUMMARY OF THE INVENTION

In light of the foregoing, it is an object of the present invention toprovide organic charge-transfer (CT) co-crystals into a mixed stacksystem, wherein a donor molecule (D) and an acceptor molecule (A) occupyalternating positions (DADADA) along the CT axis. A platform is providedwhich amplifies the molecular recognition of donors and acceptors andproduces co-crystals at ambient conditions, wherein the platformcomprises (i) a molecular design of the first constituent(α-complement), (ii) a molecular design of the second compound(β-complement), and (iii) a solvent system that promotesco-crystallization. The terms α-complement and β-complement arestructural designations that refer to the complementary recognition ofthe components. These designations are not associated with theelectronic character of the molecules, and either complement can be anelectron donor or an electron acceptor. The co-crystals disclosed hereinare not only CT pairs but are also capable of assembling into orderedthree-dimensional supramolecular networks.

Accordingly, it will be understood by those skilled in the art that oneor more aspects of this invention can meet certain objectives, while oneor more other aspects can meet certain other objectives. Each objectivemay not apply equally, in all its respects, to every aspect of thisinvention. As such, the following objects can be viewed in thealternative with respect to any one aspect of this invention.

Other objects, features, benefits and advantages of the presentinvention will be apparent from this summary and the followingdescriptions of certain embodiments, and will be readily apparent tothose skilled in the art. Such objects, features, benefits andadvantages will be apparent from the above as taken into conjunctionwith the accompanying examples, data, and all reasonable inferences tobe drawn therefrom. The disclosures in this application of all articlesand references, including patents, are incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides the structural formulas of the lock-arm supramolecular(LASO) ordering electron donors and electron acceptors used in theself-assembly of ten network solids.

FIGS. 2a-c provide images of the crystal morphology for ten LASOcrystals and the experimental controls for the crystallization; (a) tenLASO co-crystals grown from four α-complements and eight β-complements;(b) image taken after 5 days showing the co-crystals of 1α-9β grown bydiffusion 1-chlorobutane into 1,2-dichloroethane/diethyl ether,contaminated with traces of H₂O; (c) image shows experimental controlsfor the co-crystallizations grown to show that α′-arm and β-arms areessential for self-assembly of LASO materials.

FIG. 3 is a diagram illustrating the use adaptive intermolecularrecognition in the system 1α·9β.

FIG. 4 provides diagrams that slice through the crystal structures ofthe ten LASO network solids.

FIGS. 5a-c provide noncovalent connectivity diagrams depicting theglobal topology of the hydrogen bonded network for systems 1α·9β,1α·10β, and 1α·12β; (a) diagram showing the network topology of thesystem 1α·9β; (b) diagram showing the network topology of the system1α·10β; (c) diagram showing the network topology of the system 1α·12β.

FIGS. 6a-d (a) molecular structures of electron donor (1α) and electronacceptor (9β, 10β and 12β) molecules; (b) co-crystal 1α·9β belonging tothe P1 space group with unit cell spacings of 9.5063(4) Å, 12.1715(6) Å,and 12.8872(6) Å, and two unique DA pairs (1α_(A)·9β_(A), 1α_(B)·9β_(B))with spacings of 3.25 Å and 3.26 Å between the closest C—C contact; (c)co-crystal 1α·10β belongs to the Pn space group with unit cell spacingsof 6.9937(2) Å, 11.8675(2) Å, and 17.5154(3) Å; the co-crystal has a C—Cdistance of 3.30 Å for the closest contact; (d) co-crystal 1α·12β has aP2₁ space group with unit cell spacings of 11.909(6) Å, 6.959(3) Å, and16.711(7) Å, and a C—C spacing of 3.48 Å for the closest contact in theDA dimer.

FIGS. 7a-c provide noncovalent connectivity diagrams through Hirshfeldsurface analysis of (a) co-crystal 1α·9β; (b) co-crystal 1α·10β; and (c)co-crystal 1α·12β.

FIGS. 8a-f provide images showing the growth of LASO networks after 48hours for (a) co-crystal 1α·9β; (b) co-crystal 1α·10β; and (c)co-crystal 1α·12β; and optical microscopy of very thin (>10 μm)co-crystals with linearly polarized white light for (d) co-crystal1α·9β; (e) co-crystal 1α·10β; and (f) co-crystal 1α·12β.

FIGS. 9a-c provide linear dichroism of the LASO networks for (a)co-crystal 1α·9β; (b) co-crystal 1α·10β; and (c) co-crystal 1α·12β.

FIGS. 10a-c show the temperature variation of the dielectric constant ofLASO (a) co-crystal 1α·9β; (b) co-crystal 1α·10β; and (c) co-crystal1α·12β.

FIGS. 11a-g provide polarisation hysteresis curves for complex 1α·9βmeasured at (a) 300° K and (b) 74° K; polarisation hysteresis curves forcomplex 1α·10β measured at (c) and (d) 300° K and at (e) 7° K;polarisation hysteresis curves measured for complex 1α·12β at (f) 300° Kand (g) 7° K.

FIGS. 12a-b are (a) a ¹H NMR spectrum of 1α recorded at 25° C. inCD₃COCD₃ and (b) a ¹³C NMR spectrum of 1α recorded at 25° C. inCD₃COCD₃.

FIG. 13 is a polarized vibrational spectra (300° K) of the co-crystal1α·7β showing coincident Raman and IR modes.

FIG. 14 is a polarized vibrational spectra (300° K) of the co-crystal1α·8β showing coincident Raman and IR modes.

FIG. 15 is a polarized vibrational spectra (300° K) of the co-crystal1α·9β showing coincident Raman and IR modes.

FIG. 16 is a polarized vibrational spectra (300° K) of the co-crystal1α·10β showing coincident Raman and IR modes.

FIG. 17 is a polarized vibrational spectra (300° K) of the co-crystal1α·12β showing coincident Raman and IR modes.

FIG. 18 is a polarized vibrational spectra (300° K) of the co-crystal2α·9β showing coincident Raman and IR modes.

FIG. 19 is a polarized vibrational spectra (300° K) of the co-crystal2α·11β showing coincident Raman and IR modes.

FIG. 20 is a polarized vibrational spectra (300° K) of the co-crystal5α·3β showing coincident Raman and IR modes.

FIG. 21 is a polarized vibrational spectra (300° K) of the co-crystal5α·4β showing coincident Raman and IR modes.

FIG. 22 is a polarized vibrational spectra (300° K) of the co-crystal6α·3β showing coincident Raman and IR modes.

FIGS. 23a-b provide linear graphs used to determine the ionicity basedon the shifting of the ungerade modes in the IR spectra; (a) follows theshift of ν (C═C) for 12_(β); (b) follows the shift of ν (C≡N) for 4_(β).

FIG. 24 is a flow chart illustrating IR modes used to determine ρ forthe LASO co-crystals.

FIGS. 25a-d provide linear graphs used to determine the ionicity, basedon the shifting of the ungerade modes in the IR spectra; (a) follows theshift of ν (C═O) for 1_(α);

-   -   (b) follows the shift of ν (C═C) for 9_(β); (c) follows the        shift of ν (C═O) for 2_(α); and (d) follows the shift of ν (C═O)        for 3_(β).

FIG. 26 is an Oak Ridge Thermal Ellipsoid Plot (ORTEP) drawing of 1α·7β.

FIG. 27 is an ORTEP drawing of 1α·8β.

FIG. 28 is an ORTEP drawing of 1α·9β.

FIG. 29 is an ORTEP drawing of 1α·10β.

FIG. 30 is an ORTEP drawing of 1α·12β.

FIG. 31 is an ORTEP drawing of 2α·9β.

FIG. 32 is an ORTEP drawing of 2α·11β.

FIG. 33 is an ORTEP drawing of 5α·3β.

FIG. 34 is an ORTEP drawing of 5α·4β.

FIG. 35 is an ORTEP drawing of 6α·3β.

FIGS. 36a-b provide linear graphs used to determine the ionicity basedon the shifting of the ungerade modes in the IR spectra; (a) smallcrystals of complex TCNQ·10β grown and ρ for this complex used as areference to estimate the ionicity of the remaining co-crystals; (b)ionicity for 1α·9β, 1α·10β and 1α·12β determined to be 0.67, 89, and0.43, respectively.

FIG. 37 are images of complex 1α·9β and 1α·10β growing along the glassof a crystallizing container.

FIG. 38 is a graph of the temperature dependent dielectric constant ofTTF-CA (control).

FIGS. 39a-b provide graphs for magnetic hysteresis of LASO (a)co-crystal 1α·9β; and (b) co-crystal 1α·12β.

FIGS. 40a-b provide graphs for zero-field cool and field coolmagnetisation versus temperature plots for LASO(a) co-crystal 1α·9β; and(b) co-crystal 1α·12β.

FIG. 41 shows the iron analysis of solvents used in LASOco-crystallisation.

FIG. 42 shows the iron analysis of untreated compounds 1α and 9β.

FIGS. 43a-d (a) is an image of mixed powder of compounds 1α and 9β; M(H)curves at 7 K for mixed powder of compounds (b) 1α and (c) 9β; (d) ironanalysis report for mixed compound 1α and 9β.

FIG. 44 shows the iron analysis for co-crystal 1α·9β and co-crystal1α·12β.

FIGS. 45a-b are a magnetic force microscopy imaging in Lift-off Mode forco-crystal 1α·12β; (a) plots of the height (nm); and (b) frequency shiftat 80 nm.

FIGS. 46a-c (a) are a magnetic force microscopy, Z-spectroscopy plot ofrepulsive and attractive potentials across the surface of crystal1α·12β; (b) is a plot of frequency shift versus height (nm) illustratingan attractive potential; (c) is a plot of frequency shift versus height(nm) characteristic of a repulsive potential.

FIGS. 47a-c are polarization hysteresis of compound 1α·10β at (a) 7 K;(b) 150 K; and (c) 300 K.

FIGS. 48a-b are polarization hysteresis of compound 1α·12β at (a) 7 Kand up to (b) 35 K.

FIGS. 49a-b provide optical images of (a) ferroelectric device with goldpaste and wire; and (b) ferroelectric device with gold paste and wire atvoltage >900V and higher temperatures, wherein crystals melted.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, a non-limiting embodiment of the invention is an organiccharge-transfer (CT) co-crystal in a mixed stack system, wherein theco-crystal consists essentially of an electron acceptor molecule (A) andan electron donor molecule (D), wherein one of A and D is anα-complement and the other one of A and D is a β-complement, such thatthe β-complement is incorporated into the α-complement through molecularlinkages in a solvent system to form a co-crystalline supramolecularnetwork, wherein one or more of the molecular linkages between theα-complement and the β-complement use adaptive intermolecularrecognition to form the one or more molecular linkages, the co-crystalcharacterized by having a crystal superstructure comprising a mixedstack lattice (DADADA) and a topologically intricate hydrogen-bondednetwork.

In an embodiment of the invention, the α-complement makes use of abinding motif referred to as adaptive intermolecular recognition.Adaptive intermolecular recognition is defined as the use ofconformational isomerism (flexibility) by a molecule to alter thespatial distribution of its recognition sites to achieve energeticallystable intermolecular binding in a solid supramolecular network(Aakeroy, C. B., et al. Crystengcomm 2010, 12, 22-43 and Moulton, B., etal. Chem. Rev. 2001, 101, 1629-1658, both incorporated herein byreference). The structure of a molecule that exhibits adaptiveintermolecular recognition has two distinguishing criteria, (i)conformational flexibility (this term excludes hydrogen atoms as well assmall distortions of molecular geomtery associated with lattice packing,as for example, bond lengthing or the deviation of an aromatic ring fromplanarity); and (ii) recognition sites that have a unique distributionof distances relative to the molecular centroid for every conformationalisomer (FIG. 5). The use of conformational flexibility to achieveintermolecular binding (adaptive intermolecular recognition) in thelattice distinguishes the co-crystals described herein from networksolids utilizing rigid molecules whose recognition sites have a fixeddistance with respect to the molecular centroid, e.g. coordinationpolymers and metal organic frameworks.

As described herein, 1α, 2α, 5α, and 6α, have the conformationalflexibility needed for adaptive intermolecular recognition. 1α is a goodillustration of how adaptive intermolecular recognition is used in thesystems described herein. It has two flexible diethylene glycolappendages (FIG. 1). Each appendage (or α′-arm) has two recognitionsites for hydrogen bond (H-bond) formation, i.e., an ether oxygen atomand a hydroxyl group. In co-crystals which contain 1α, the moleculesthat neighbor 1α also have supramolecular recognition sites (Desiraju,G. R. Angew. Chem. Int. Ed. 1995, 34, 2311-2327, incorporated herein byreference) (C═O, —NH₂, —OH), and the glycol appendages “reach” for themto form the most thermodynamically stable H-bonds (FIG. 3 and FIG. 4).As a result, the conformations of the glycol chains adapt to the spatialpositions of local recognition sites with the conformational changes,depending on the donor used in the co-crystal (FIG. 5).

To initiate the self-assembly, the α-complements (α) are paired with asmaller CT partner (donor or acceptor) with one or more rigid H-bondrecognition sites such as amino, carbonyl, ether and hydroxyl moieties(FIG. 2 and FIG. 3) called the β-complement (β). The only β that iscapable of adaptive intermolecular recognition is 12β. This fact makes1α·12β unique since both constiuents engage in adaptive intermolecularrecognition. In the crystallizing solution, the α and β associatethrough CT. It is believed, however, that the complementary H-bondinginteractions between the flexible and rigid moieties on α and β drivethe molecules to self-assemble into an energetically stable networksolid.

In another embodiment of the invention, the methods used to produce theco-crystals of the invention should preferably exercise a stronginfluence on the self-assembly of α and β. When a mixture of α and β iscombined in the optimal solvent system, expedient self-assembly underambient conditions should be observed. The dependence of amplifiedco-crystal growth on the solvent suggests that the crystallizationsolution promotes the self-assembly of the constituents. The solventsystem can be one solvent or a mixture of solvents. The solvent(s) is,preferably, an organic solvent. In a more preferred embodiment, Table 1provides examples of solvent systems employed by the methods forproducing the co-crystals.

TABLE 1 Molar Growth Co- Concentration^(a) Ratio Time Crystal SolventSystem (mg/mL) (β:α) (d) 1α·9β Dichloroethane/ 2 2 3 Diethyl Ether(200/1) 1α·10β Dichloroethane/ 1.5 2 3 Diethyl Ether (200/1) 1α·12βDichloroethane/ 1 2 3 Diethyl Ether (200/1) 1α·7β Dichloroethane/ 1.5 23 Diethyl Ether (200/1) 1α·8β Dichloroethane/ 1.5 2 3 Diethyl Ether(200/1) 2α·9β Dichloroethane/ 2 15^(b ) 3 Diethyl Ether (200/1) 2α·11βDichloroethane/ 1 2 3 Diethyl Ether (200/1) 6α·3β N- 2 2 5Methylpyrrolidone 5α·3β Dichloroethane/ 2 2 3 Diethyl Ether (200/1)5α·4β N- 2 2 5 Methylpyrrolidone ^(a)Concentration of the electronacceptor (α or β) in the crystallizing solution only. ^(b)Concentrationneeded to initiate self-assembly.

As used herein, the self-assembly platform producing the co-crystals isreferred to as Lock-Arm Supramolecular Ordering (LASO). A LASO networksolid is defined as a crystalline supramolecular network wherein one ormore of the molecular linkages use adaptive intermolecular recognitionto bind to its neighboring molecules. The crystal superstructures (FIG.4) of the LASO networks used herein constitute a combination of a mixedstack lattice and a topologically intricate H-bonded network.Preferably, the αs and βs are tightly packed and the crystals are devoidor substantially devoid of solvent. Also preferably, the use of the LASOplatform is applied to diimide acceptors.

The D and A components used in co-crystal systems are shown in FIG. 1.As used herein, the ring system of a molecule is the “frame” (FIG. 3),and any appendage extending from the frame that has a supramolecularbinding site is an “arm”. For simplicity, aromatic hydrogen atoms on theframe will not be classified as arms. In addition to arms, therecognition sites, such as the sulfur atoms in 12β, are incorporatedinto the frame and are referred to as “sites”. The nitrogen atoms in thediimide molecule are sterically hindered hydrogen bond acceptors and aretherefore not considered sites. In a LASO co-crystal, both complementarymolecules, i.e., α and β (FIG. 4) have arms (FIG. 3). The α is themolecule that contains the longest conformationally flexible armextending from the frame (measured by the number of atoms). Thisappendage is called the α′-arm. The α can have one or more, andpreferably two or more, arms, and even more preferably four or morearms, of which at least one, and preferably two, is an α′-arm. All otherarms are denoted without the prime symbol, e.g., the shorter β-arms onthe β or the rigid C═O α-arms extending from the α frame (FIG. 1 andFIG. 3). The β is the molecule with one or more, preferably at leasttwo, shorter arms that is incorporated into the supramolecular frameworkof a LASO network solid through molecular recognition with α. Thestructures in FIG. 1 are the αs and βs that are used to create the LASOsystems (FIG. 2a and FIG. 4) described herein. In the specificnon-limiting examples of FIG. 1, there are four αs, two six-arm electronacceptors (1α, 2α) and two, two-arm electron donors (5α, 6α). All the ashave a pair of similar α′-arms based on a diethylene glycol moiety, butin addition to the α′-arm, 1α and 2α also have four shorter carbonylα-arms. For the βs, two electron acceptors (3β, 4β) and six electrondonors (7β-12β) are used. Acceptors 3β and 4β are six-arm and four-armβs, respectively. Donors 7β-10β are all two-arm βs, while 11β is aone-arm β. The donor molecule 12β is the most distinct of the βs. It hastwo R═CH₂OH β-arms, and four sulfur sites making it a two-arm, four-siteβ.

Turning to the ferroelectric behavior of specific embodiments, the CTcrystals disclosed herein are based on complexes between donors thatare, for example, derivatives of a pyromellitic diimide-based acceptor(FIG. 6a ). These CT pairs are co-crystallised (FIG. 8a-8c ) underambient conditions and the resulting solid state structurescharacterized by X-ray crystallography (FIG. 6b-6d ). The basicstructural details for each lattice are summarized in Table 2. In thesenetworks, the assembly of the acceptor 1α and donor (9β, 10β, 12β)components in the lattice are stabilized by four primary supramolecularinteractions: (i) charge transfer (CT), (ii) hydrogen bonding, (iii) π-πstacking, and (iv) van der Waals forces. Diimide 1α is functionalizedwith diethylene glycol arms that are capable of acting as both hydrogenbond donors and acceptors. Electron-rich compounds 9β, 10β, 12β can alsointeract through hydrogen bonding since their shorter arms areterminated by hydroxyl or amino groups. An extensive hydrogen bondednetwork comprised of interstack and intrastack hydrogen bonds (FIG.6b-6d ) is formed during the self-assembly process. This LASO enablescomplementary molecules to crystallize rapidly into functional networksfrom solution under ambient conditions (FIG. 7a-7c ). The overall motiffor LASO structures requires a hierarchical organization based onnoncovalent bonding interactions that bridge distances from Angstroms tonanometres and are considerably stronger than van der Waals forces.Locally, the CT and n-n stacking interactions are directed along asingle dimension parallel to the mixed stack axis, while the hydrogenbonds extend into three dimensions. This panoply of supramolecularinteractions leads to a tightly packed network of mixed stacks lockedover larger length scales by hydrogen bonds, π-π stacking, and CT.

TABLE 2 1α9β 1α10β 1α12β formula C₂₈H₃₀N₄O₈ C₃₄H₃₂N₄O₈ C₂₆H₂₈N₂O₁₀S₄ M550.56 624.64 656.77 Crystal triclinic monoclinic monoclinic systemSpace P1 Pn P2₁ Group a (Å)  9.5063 (4)  6.9937 (2) 11.9236 (4) b (Å)12.1715 (6) 11.8675 (2)  6.9553 (3) c (Å) 12.8872 (6) 17.5154 (3)16.7123 (5) α (deg.)  61.896 (3) 90.00 90.00 β (deg.)  89.095 (3)100.896 (1) 104.157 (2) γ (deg.)  76.689 (3) 90.00 90.00 V (Å³) 1272.50(1) 1427.53 (5) 1343.89 (8) Z 2 2 2 T (K) 84 100 85

In order to illustrate the connectivity of the hydrogen bonded networkin the interstitial regions between the stacks, Hirshfeld surfaceanalysis (McKinnon, J. J., et al. Acta Crystallogr., Sect. B: Struct.Sci 2004, 60, 627-668, incorporated herein by reference) is used tomeasure the distribution of close contact interactions (FIG. 7). TheHirshfeld surface is a graphical tool that compares the atomicallyaveraged electron density of a molecule to the electron density of theentire crystal and partitions the lattice into molecular surfaces whichmap the spatial contacts. In FIG. 7, white regions represent molecularcontacts at the van der Waals distance, while grey and black portionsrepresent lengths shorter and longer than the van der Waals distance,respectively. This type of analysis helps identify which interactionsare the most dominant among neighbouring stacks. The bar graphs showthat [O . . . H] interactions responsible for hydrogen bonding make up37-41% of all interstack contacts while [H . . . H] interactions are42-50% of such contacts, revealing the close packed nature of thestructure (FIG. 7). The lengths shorter than van der Waals aresignificant because they arise from short [O . . . H] and [H . . . H]distances when interstack hydrogen bonds are formed. These interstackinteractions are between neighboring arms and allow the stacks to packtightly into a supramolecular network.

Since the electron transfer occurs along the stacking axis, ionicity(ρ), the extent of CT, is characterized to investigate how its magnitudeaffects ferroelectric behavior. Polarized vibrational spectroscopy(FT-IR) is used to determine ρ for each compound. The ungerade modes areused to calculate ρ because they are not influenced byelectron-molecular vibration interactions. At room temperature, ρ for1α9β, 1α10β, and 1α12β is determined by following the linear shift ofthe C═O stretch (1728-1716 cm⁻¹) polarized parallel to the DA stack.Compounds 1α9β and 1α10β are measured to be ionic with ρ=0.68 and 0.89(see Table 3 below), respectively, while 1α12β lies close to theneutral-ionic border (ρ=0.5) with ρ=0.43. Therefore, the polar nature ofthe crystal enables the LASO network to be ferroelectric. Along withsignificant electron transfer, a violation of the mutual exclusion rulebetween the IR and Raman modes exists in all three systems at 300° K,indicating a non-centrosymmetric lattice. This behavior in mixed stackcrystals, comprised of symmetric molecules, demonstrates that LASOnetworks fulfill the requirements for a ferroelectric system, namely, DAdimerization and a polar lattice.

Polarized UV-Vis transmission spectroscopy (Kuwatagonokami, M. et al.Nature 1994, 367, 47-48, incorporated herein by reference) (FIG. 9a-9c )and polarized optical microscopy (FIG. 8d-8f ) are employed to elucidatethe anisotropy of the CT in LASO networks with regard to the crystalaxis. When the linear polarization of white light is oriented parallelto the polar mixed stack (long axis), the system absorbs intensely.Conversely, when the polarization is oriented perpendicular to the stackaxis, there is a clear lack of color. The absorbance bands (FIG. 9a-9c )associated with this color change shows a maximum in absorbance when thepolarization is aligned with the direction of the stacks for 1α9β,1α10β, and 1α12β. These transitions (FIG. 9a-9c , inset) located between1.38-1.50 eV (800-900 nm) are attributed to the lowest intra-dimer CTexciton state (Meneghetti, M., et al. J. Chem. Phys. 1996, 105, 397-407,incorporated herein by reference) (DA^(δ+)A^(δ−)□ [D^(δ+)A^(δ−)]*).Based on this pronounced dichroism, it is possible to establishunequivocally that the polar axis of the material is aligned with thelong axis of the crystal.

To determine the ferroelectric Curie temperature of each structure, thedielectric constant (∈_(r)) is measured as a function of temperaturealong the ferroelectric axis. For co-crystals 1α9β, 1α10β, and 1α12β, nocharacteristic discontinuity is observed between 5° K and 400° K (FIG.10a-10c ). These results suggest that the ferroelectric phase exists atroom temperature, an observation which is consistent with spectroscopicand crystallographic evidence. The temperature dependent dielectricconstant measurements are performed on TTF-CA as a control (FIG. 38).This measurement shows a T_(c) of 84° K, consistent with previouslyreported studies of ferroelectric phase transitions. Further evidencefor room temperature ferroelectricity is obtained by measuringhysteresis curves of electric displacement versus electric field (D-E)along the ferroelectric axis (FIGS. 11a, 11c, and 11f ). Polarizationhysteresis curves for co-crystal 1α9β are measured at 300° K (FIG. 11a )and 74° K (FIG. 11b ). Polarization hysteresis curves for complex 1α10βare measured at 300° K (FIGS. 11c and 11d ) and at 7° K (FIG. 11e ).Polarization hysteresis curves are measured for complex 1α12β at 300° K(FIG. 11f ) and 7° K (FIG. 11g ). Room temperature hysteresis curves forLASO complexes are underpolarized because of leakage currents at highvoltage. Ferroelectric network 1α10β shows hysteresis similar to 1α9βand 1α12β at small electric fields (FIG. 11d ). At larger electricfields, 1α10β demonstrates larger hysteresis loops (FIG. 11c ). Theunexpectedly large remnant polarisation in 1α12β observed at lowtemperatures is attributed to a combination of charge transfer exchangeand proton dynamics within the lattice. Hysteresis curve measurementsare performed at f=0.1 Hz for FIGS. 11a -e, g, and f=1 Hz for FIG. 11f .Polarization hysteresis of co-crystals 1α9β, 1α10β, and 1α12β areobserved at 300° K with remnant polarizations (P_(r)) exceeding 1μC/cm². Attempts to observe saturation by applying higher electricfields results in dielectric breakdown and crystal melting. Largerpolarization hysteresis loops are obtained at lower temperatures down to7° K where leakage currents are minimized (FIG. 11b, 11d, 11e and 11g ).At low temperature, D-E curves for co-crystal 1α12β are unexpectedlylarge. Surprisingly, the P_(r) for this network is found to beapproximately 55 μC/cm², much larger than compound 1α9β or 1α10β. Thislarge polarization can result from the combination of the CT process andproton dynamics within the crystal (Horiuchi, S., et al. Nature Mater.2008, 7, 357-366 and Horiuchi, S., et al. Nature 2010, 463, 789-797,both incorporated herein by reference). The P_(r) of 1α11β at 7° K isamong the highest reported for organic ferroelectrics based on chargetransfer, hydrogen bonding, liquid crystalline or polymeric materials.The resistivity of all LASO systems investigated, however, is found tobe very high (>10⁹ Ω/cm) at room temperature.

The ferroelectric curves obtained at room temperature are biased at alower electric field compared to cryogenic temperatures. At highelectric fields at room temperature, dielectric leakage and jouleheating prevents the measurement of saturating polarization hysteresisloops. Curves measured at 300° K are obtained by applying a smallerelectric field than required for saturation. As a result, these systemsare inherently under-polarized and have smaller remnant polarizationsthan saturated loops.

Larger hysteresis loops are obtained in compound 1α10β (FIG. 11d ) atroom temperature because this network is able to withstand highervoltages. It is interesting to note that this hydrogen bonded networkhas a higher ionicity (ρ˜0.89) than co-crystals 1α9β or 1α12β. The onlyCT ferroelectric that demonstrates polarization bistability is TTF-BAwith a T, of 53° K. TTF-BA also has a very large ionicity with ρ˜0.9,similar to 1α10β. As pointed out by Torrance, J. B. Accounts of ChemicalResearch 1979, 12, 79-86, incorporated herein by reference, highionicities inhibit current flow in CT crystals because of Coulombicinteractions. Negative and positive ions in a lattice can behave asionic impurities that actively scatter moving electrons. Network 1α10βand TTF-BA have large ionicities and may therefore mitigate leakagecurrent to some degree. In this context, developing networks of CTcomplexes with large ionicities may be a useful design rule forferroelectricity at room temperature and above.

Ferroelectric networks 1α9β and 1α12β are characterized by SQUIDmagnetometry and revealed magnetic hysteresis loops. Extensive elementalanalysis described in detail below shows that any magnetic impuritiespresent have to be below the detection limit of currently availableinstruments for inductively coupled plasma atomic emission spectroscopy(ICP-AES). Other measurements (Magnetic Force Microscopy) describedbelow attempt to verify ferromagnetic behavior.

Materials and Methods

All compounds are purchased from commercial vendors (Sigma Aldrich andVWR) and are used as supplied without further purification. For thesynthesis of 1α, 2α, 5α, 6α, and 12β see: Bevers, S., et al. J. Am.Chem. Soc. 2000, 122, 5905-5915; Sue, C. H., et al. Chem Sci 2010, 1,119-125; Asakawa, M., et al. Journal of Organic Chemistry 1996, 61,9591-9595; and Saha, S., et al. Chem. Eur. J. 2005, 11, 6846-6858, allincorporated herein by reference.

All the crystals are grown in the dark, under ambient conditions usingliquid diffusion. Two distinct solvent systems are found to promoteexpedient crystal growth. The molar ratio α:β and the totalconcentration of α+β are optimized to achieve the best crystal size andgrowth rate (Table 1). The eight co-crystals which do not contain 3β(pyromellitic diimide) are grown from liquid diffusion of anhydrousnon-protic solvents 1-chlorobutane into a 1,2-dichloroethane and diethylether mixture (FIG. 2a and FIG. 3). As H₂O is found to disrupt theself-assembly of these eight co-crystals, anhydrous conditions for thematerials and solvents are ensured before the crystals are grown. Owingto the insolubility of 3β in common organic solvents, a different typeof solvent combination is used for the two complexes containing β. Theliquid diffusion of protic H₂O into polar N-methylpyrrolidone is foundto produce the most pronounced crystal growth. EG/SiC samples areproduced in a UHV chamber with a base pressure below 1×10⁻¹⁰ Torr unlessotherwise noted. The SiC is resistively heated by passing currentthrough the SiC while temperatures are monitored using an opticalpyrometer (Cyclops) at an emissivity of 0.85. The SiC is degassedovernight at 600° C. and then annealed for 2 minutes at 1000° C. The SiCis then flashed 3 times at 1100° C. for 2 minutes each. After eachflash, the sample is allowed to cool for 10 minutes. Finally, the SiC isgraphitized at 1300° C. for 2 flashes and then 10 flashes at 1350° C.for 1 minute apiece.

Thin layer chromatography (TLC) is performed on silica gel 60 F254 (E.Merck). Nuclear magnetic resonance (NMR) spectra are recorded at 25° C.on Varian Inova 500 spectrometers, with working frequencies of 500 MHzfor ¹H, and 125 MHz for ¹³C nuclei (see FIG. 12a and FIG. 12b for ¹H and¹³C NMR, respectively, of 1α). The chemical shifts are listed in ppm onthe δ scale and coupling constants are recorded in Hertz (Hz). Thefollowing abbreviations are used to explain the multiplicities: s,singlet; d, doublet; t, triplet; b, broad peaks; m, multiplet oroverlapping peaks. High resolution electrospray ionization (HR ESI) massspectra are measured on a Micromass Q-TOF Ultima mass spectrometer. AllFT-IR spectra are collected by a Perkin Elmer Spectrum Spotlight ImagingSystem utilizing liquid nitrogen cooled single elementmercury-cadmium-telluride detector in single-point reflectance mode withan aperture setting of 50×50 μm². The sample is presented as a singlecrystal placed on a Si plate. Raman spectra are obtained with either anAdvantage 532 Raman Spectrometer using a 532 nm excitation line or a 633nm HeNe laser (Research Electro-Optics Inc.) that collects the scatteredlight into a spectrograph (PI Acton SP2500i) equipped with a 600 g/mmgrating blazed at 750 nm and a liquid-N₂ cooled CCD detector.Polarization of the HeNe laser is achieved using an adjustable airspaced achromatic half-wave waveplate (CVI Melles GriotACWP-400-700-10-2). A baseline correction is performed to allow forinterpretation of the spectra. Single crystals of the complexes aremounted in oil (InfineumV8512) on a glass fiber under a nitrogen coldstream at 83(2) ° K. X-Ray diffraction data are collected on a BrukerKappa diffractometer, equipped with a CuKα or MoKα sealed-tubesource andan APEX II CCD detector. Data are collected, integrated and correctedfor decay and Lp effects using BrukerAPEX II software. Final unit cellparameters are obtained through a refinement of all observed reflectionsduring data integration. A multi-scan absorption correction is performedusing SADABS. The structures are solved and refined using the SHELXTLsuite of software. The absorption spectra are taken using a polarizationmicroscopy setup. A Nikon TE2000 inverted microscope and Prior ProScanII stage are used to manipulate the sample position. The microscopehalogen lamp is used as the source for the absorption spectra. Spectraare recorded using an Ocean Optics USB 2000 miniature spectrometer. Thepolarization dependence is varied using a thin film polariser. Cyclicvoltammetry (CV) and square-wave differential pulse voltammetry (SWDPV)experiments are performed at room temperature in argon-purged solutionsof N,N′-dimethylformamide (DMF) with a Gamry Multipurpose instrument(Reference 600) interfaced to a PC. The CV and SWDPV experiments in eachcase are performed using a glassy carbon working electrode (0.071 cm²).The surface of this electrode is polished routinely with 0.05 μmalumina-water slurry on a felt surface immediately before each run. Thecounter electrode is a Pt coil and the reference electrode is asaturated calomel electrode (SCE) for both CV and SWDPV experiments. Theconcentration of the sample and supporting electrolytetetrabutylammonium hexafluorophosphate (TBA-PF₆) are 1.0×10⁻³ mol·L⁻¹and 0.1 mol·L⁻¹, respectively. The scan rate for CV experiments is setto 200 mV·s⁻¹. Experimental errors: potential values, ±10 mV for CV and±1 for SWDPV.

Ferroelectric structures are mechanically robust and can be handled withvacuum tweezers. Gold wire electrodes (12.5 μm) are attached on eitherend using gold paint (Ted Pella Gold Paste). The resulting devices aretested in a QuantumDesign PPMS 6000 under an inert atmosphere. Thedielectric constant of LASO complexes is determined bycapacitance-voltage measurements at 10 V with a 1, 5, or 10 kHzfrequency. These measurements are performed using an Agilent E4980A LCRmeter. Polarization hysteresis is measured using a ferroelectric testerat 0.1 Hz or 1 Hz frequency (Radiant Technologies Precision LC with Trekamplifier).

Vibrational spectroscopy data helps elucidate the lattice symmetry ofthe co-crystals at ambient conditions. Six of the LASO crystals arerefined in centrosymmetric space groups. The remaining four co-crystals(1α·9β, 1α·10β, 1α·12β, 5α·3β), however, are found to adopt anon-centrosymmetric lattice. These network solids have the spectroscopicsignature of a mixed stack crystal that has undergone a polar phasetransition where the donors and acceptors have dimerized (D⁰ A⁰ D⁰ A⁰ □D^(+ρ)A^(−ρ) D^(+ρ)A^(−ρ)) along the charge transfer (CT) axis.

Employing IR and Raman spectroscopic techniques, the details of theground state for a CT crystal are experimentally accessible (See FIGS.13-23). In segregated stacks, totally symmetric (ts) modes can be usedto measure the value of the ionicity (ρ) for the material (Girlando, A.,et al. Synth. Met. 2004, 141, 129-138, incorporated herein byreference), but in mixed stack systems the ts modes are perturbed by theelectron-molecular vibration interaction (Girlando, A., et al. J. Chem.Phys. 1983, 79, 1075-1085, incorporated herein by reference) and are notuseful for this purpose. However, because the ts Raman modes ofmolecules in crystals are subject to the selection rules governed bysite symmetry, these bands are good probes for the loss ofcentrosymmetry. When molecules do not occupy a center of inversion, thets vibrations can violate the principle of mutual exclusion (Nakamoto,K. Infrared and Raman Spectra of Inorganic and Coordination Compounds,6th ed., Wiley [Oxford Wiley-Blackwell, distributor]: Hoboken, N.J.,2009, incorporated herein by reference) and appear in the IR spectrum.Away from the center of inversion the molecular dipole moment can changewith ts vibrations about its equilibrium. In a polar mixed stack systemwith symmetric molecules, the dimerization of the donor and acceptorbreaks the inversion symmetry in the lattice, and the donor and acceptorno longer reside on inversion centers. The ts modes are now capable ofproducing an asymmetric charge distribution (dipole moment) and stronglycoupling to the CT along the stack. As a result, the ts modes can becomecoincident in their IR and Raman spectra and are strongly polarized inthe direction of the CT axis. Most of the co-crystals have somecoincident bands (ν(CH₂)) in the Raman and IR spectra, but only four(FIG. 5, FIG. 6, FIG. 7 and FIG. 10) of the LASO co-crystals displaythis spectroscopic signature in regions (ν(C═O), ν(C═C)) that aresensitive to the CT interaction.

Referring to FIGS. 13-23, provided are the polarized vibrational spectra(300 K) of co-crystals showing coincident Raman and IR modes. The lowestplot is the unpolarized Raman spectrum. The symbols ρ and ⊥ indicatelinear polarization of the IR radiation with the electric field orientedparallel and perpendicular to the CT stack, respectively. The 1α·7βco-crystal is a crossed stack system (FIG. 13); the 1α·8β co-crystal isa crossed stack system, and the lattice also contains and asymmetric β(FIG. 14); the violation of the rule of mutual exclusion, aspectroscopic signature of dimerization in co-crystal 1α·9β (FIG. 15);the violation of the rule of mutual exclusion, a spectroscopic signatureof dimerization in co-crystal 1α·10β (FIG. 16); the violation of therule of mutual exclusion, a spectroscopic signature of dimerization inco-crystal 1α·12β (FIG. 17); co-crystal 2α·9β shows very few coincidentpeaks, indicating a lack of dimerization between the donor and acceptor,possibly caused by the positional disorder found in the lattice (FIG.18); co-crystal 2α·11β contains an asymmetric β that could result in theoverlap of modes between the IR and Raman spectra (FIG. 19); theviolation of the rule of mutual exclusion, a spectroscopic signature ofdimerization in co-crystal 5α·3β (FIG. 20); co-crystal 5α·4β shows veryfew coincident peaks, indicating a lack of dimerization between thedonor and acceptor, possibly caused by the positional disorder found inthe lattice (FIG. 21); co-crystal 6α·3β shows very few coincident peaks,indicating a lack of dimerization between the donor and acceptor,possibly caused by the positional disorder found in the lattice (FIG.22).

Since Girlando, A., et al. J. Chem. Phys. 1983, 79, 1075-1085establishes that the degree of CT (p) can be probed through the shiftsof ungerade fundamental modes in the vibrational spectra, IRspectroscopy is used extensively for this purpose. Ungerade modes arethe best choice for determining ρ, because the shift is not affected byelectron-phonon coupling. As long as the crystal is not close to theCurie temperature of a phase transition, the relationship between theshifts in these modes and changes in p are nearly linear. Linearinterpolation between the peak positions of the neutral and fullycharged molecular species—donor or acceptor—yields a reliable estimateof ρ.

To determine ρ in the LASO co-crystals, a method based on the linearshifting of the ungerade modes is also used (FIG. 23 and FIG. 36).However, a complex between 4β (tetracyanoquinodimethane, TCNQ) and thetetrathiafulvalene (TTF) derivative 12β is grown and used as a referenceto estimate p for the rest of the LASO crystals. The affect of CTinteractions on the vibrational spectra of TCNQ are well understood(Bozio, R., et al. J. Chem. Soc., Faraday Trans. II 1978, 74, 235-248;and Meneghetti, M., et al. J. Chem. Phys. 1985, 83, 3134-3145,incorporated herein by reference) and the ionicity of a co-crystal canbe determined by using the shift of the ν(C≡N) mode (FIG. 23b ). Thisprocedure is used to estimate ρ for TCNQ·4 (FIG. 23a and FIG. 36a ),ρ=1.0. In the IR spectra of the LASO co-crystals, it is found that the ν(C═O) mode in 1α is sensitive to changes in ρ (Horiuchi, S., et al. Nat.Mater. 2005, 4, 163-166, incorporated herein by reference). Usingextrapolation in the plot of ρ vs. ν (C═O) of 1α and 1α12β (FIG. 36b ),the ionicity of 1α9β and 1α10β is determined to be ρ=0.68 and ρ=0.89,respectively. FIG. 24 is a flow chart illustrating which IR modes areused to determine p for the LASO co-crystals described herein. FIG. 25contains linear graphs used to determine the ionicity based on shiftingthe ungerade modes in the IR spectra. FIG. 25a is a graph that followsthe shift of ν (C═O) for 1α; FIG. 25b follows the shift of ν (C═C) for9β; FIG. 25c follows the shift of ν (C═O) for 2α; and FIG. 25d followsthe shift of

ν (C═O) for 3β.

X-ray crystallographic data is obtained for co-crystals and are asfollows.

A) 1α·7β: C₄₆H₄₈N₄O₁₈, M=472.44, triclinic, a=6.7868(1), b=10.8904(2),c=15.7778(2) Å, α=70.880(1), β=81.554(1), γ=83.156(1)°, V=1086.72(3) Å³,T=100(2) K, space group P1, Z=1, ρ=1.44 g·cm⁻³, μ(Mo_(Kα))=0.11 mm⁻¹,10415 independent observed reflections, 6720 reflections with I>2σ(I),R_(int)=0.040, R[F²>2σ(F²)]=0.052, wR(F²)=0.132.

FIG. 26 is the Oak Ridge Thermal Ellipsoid Plot Program (ORTEP) forco-crystal 1α·7β. The hydrogen atoms are omitted for clarity. Thisco-crystal is crossed stack. The ratio of the PMDI-based α to thenaphthalene-based β is 2:1 acceptor in the unit cell. There isπ-face-to-π-face packing and edge-to-π-face packing between the α and β.All ellipsoids are displayed at the 50% probability level.

B) 1α·8β: C₄₆H₄₉N₅O₁₇, M=471.95, triclinic, a=6.7603(7), b=10.8522(11),c=15.785(2) Å, α=71.882(9), β=81.810(9), γ=84.105(8)°, V=1087.3(2) Å³,T=84(2) K, space group P1, Z=1, ρ=1.44 g·cm⁻³, μ(Mo_(Kα))=0.94 mm⁻¹,4368 independent observed reflections, 3222 reflections with I>2σ(I),R_(int)=0.047, R[F²>2σ(F²)]=0.051, wR(F²)=0.147.

FIG. 27 is the ORTEP for co-crystal 1α·8β. The hydrogen atoms areomitted for clarity. Co-crystal 1α·8β is crossed stack. The ratio of thePMDI-based α to the naphthalene-based β is 2:1 acceptor in the unitcell. There is π-face-to-π-face packing and edge-to-π-face packingbetween the α and β. 11 ellipsoids are displayed at the 50% probabilitylevel.

C) 1α·9β: C₂₈H₃₀N₄O₈, M=550.56, triclinic, a=9.5063(4), b=12.1715(6),c=12.8872(6) Å, α=61.896(3), β=89.095(3), γ=76.689(3)°, V=1272.50(10)Å³, T=84(2) K, space group P1, Z=2, ρ=1.44 g·cm⁻³, μ(Mo_(Kα))=0.11 mm⁻¹,10748 independent observed reflections, 7435 reflections with I>2σ(I),R_(int)=0.038, R[F²>2σ(F²)]=0.052, wR(F²)=0.146.

FIG. 28 is an ORTEP drawing of co-crystal 1α·9β. The hydrogen atoms areomitted for clarity, co-crystal 1α·9β is crossed stack. The ratio of thePMDI-based α to the naphthalene-based β is 2:1 acceptor in the unitcell. There is π-face-to-π-face packing and edge-to-π-face packingbetween the α and β. The β is asymmetric with amino and hydroxy armsoccupying the 1,5-positions. This asymmetry results in substitutionaldisorder at the 1,5-positions in the lattice. All ellipsoids aredisplayed at the 50% probability level.

D) 1_(α)·10_(β): C₃₄H₃₂N₄O₈, M=624.64, monoclinic, a=6.9937(2),b=11.8675(2), c=17.5154(3) Å, β=100.896(1)°, V=1427.53(5) Å³, T=100(2)K, space group Pn, Z=2, ρ=1.46 g·cm⁻³, μ(CU_(Kα))=0.87 mm⁻¹, 3273independent observed reflections, 2998 reflections with I>2σ(I),R_(int)=0.024, R[F²>2σ(F²)]=0.048, wR(F²)=0.142.

FIG. 29 is an ORTEP drawing of co-crystal 1α·10β. The hydrogen atoms areomitted for clarity. Co-crystal 1α·10β is crossed stack. The ratio ofthe PMDI-based α to the naphthalene-based β is 2:1 acceptor in the unitcell. There is π-face-to-π-face packing and edge-to-π-face packingbetween the α and β. All ellipsoids are displayed at the 50% probabilitylevel.

E) 1α·12β: C₂₆H₂₈N₂O₁₀S₄, M=656.74, monoclinic, a=11.9236(4),b=6.9553(3), c=16.7123(5) Å, β=104.227(4)°, V=1348.26(1) Å³, T=85(2) K,space group P2₁, Z=2, ρ=1.62 g·cm⁻³, μ(CU_(Kα))=3.81 mm⁻¹, 3213independent observed reflections, 2680 reflections with I>2σ(I),R_(int)=0.040, R[F²>2σ(F²)]=0.045, wR(F²)=0.130.

FIG. 30 is an ORTEP drawing of co-crystal 1α·12β. The hydrogen atoms areomitted for clarity. There is one

TTF-based β and one PMDI-based α in the unit cell. All ellipsoids aredisplayed at the 50% probability level.

F) 2α·9β: C₃₂H₂₈N₄O₈ M=596.58, triclinic, a=6.9510(2), b 8.6966(2),c=12.1281(3) Å, α=72.093(2), β=76.054(2), γ=80.941(2)°, V=674.30(3) Å³,T=100(2) K, space group PI, Z=2, ρ=1.47 g·cm⁻³, μ(Mo_(Kα))=0.11 mm⁻¹,3880 independent observed reflections, 2075 reflections with I>2σ(I),R_(int)=0.057, R[F²>2σ(F²)]=0.076, wR(F²)=0.255.

FIG. 31 is an ORTEP drawing of co-crystal 2α·9β. The hydrogen atoms areomitted for clarity. There is one naphthalene-based β and onenaphthalene diimide-based (NPDI) α in the unit cell. There is positionaldisorder in the glycol α′-arm and the ring system of β. All ellipsoidsare displayed at the 50% probability level.

G) 2α·11β: C₃₈H₃₃N₃O₈, M=659.67, triclinic, a=10.9811(8), b=12.4287(8),c=12.9441(9) Å, α=94.620(5), β=112.518(5), γ=109.840(5)°, V=1489.33(18)Å³, T=85(2) K, space group PI, Z=2, ρ=1.47 g·cm⁻³, μ(Cu_(Kα))=0.86 mm⁻¹,4883 independent observed reflections, 3441 reflections with I>2σ(I),R_(int)=0.042, R[F²>2σ(F²)]=0.058 wR(F²)=0.176.

FIG. 32 is an ORTEP drawing of co-crystal 2α·11β. The hydrogen atoms areomitted for clarity. There is one asymmetric pyrene-based β and twocrystallographically unique NPDI αs in the unit cell. The β has oneamino arm at the 1-position. The asymmetry of the β results insubstitutional disorder at the 1,8-positions within the lattice. Allellipsoids are displayed at the 50% probability level.

H) 5α·3β: C₂₈H₃₀N₄O₈, M=550.56, monoclinic, a=6.6667(3), b=23.3906(10),c=8.3455(3) Å, ρ=104.657(3)°, V=1259.03(9) Å³, T=84(2) K, space groupPc, Z=2, ρ=1.45 g·cm⁻³, μ(CU_(Kα))=0.11 mm⁻¹, 6787 independent observedreflections, 3829 reflections with I>2σ(I), R_(int)=0.080,R[F²>2σ(F²)]=0.059, wR(F²)=0.141.

FIG. 33 is an ORTEP drawing of co-crystal 5α·3. The hydrogen atoms areomitted for clarity. There is one PMDI β and one napthalene-based α inthe unit cell. All ellipsoids are displayed at the 50% probabilitylevel.

I) 5_(α)·4_(β): C₃₀H₃₀N₆O₄, M=538.60, triclinic, a=6.8961(2),b=8.0293(3), c=12.3435(4) Å, α=89.213(1), β=83.730(2), γ=73.487(2)°,V=651.25(4) Å³, T=100(2) K, space group PI, Z=1, ρ=1.37 g·cm⁻³,μ(Cu_(Kα))=0.76 mm⁻¹, 2233 independent observed reflections, 2176reflections with I>2σ(I), R_(int)=0.018, R[F²>2σ(F²)]=0.031,wR(F²)=0.084.

FIG. 34 is and ORTEP drawing of co-crystal 5α·4β. The hydrogen atoms areomitted for clarity. There is one TCNQ β and one naphthalene-based α inthe unit cell. All ellipsoids are displayed at the 50% probabilitylevel.

J) 6α·3β: C₂₈H₂₈N₂O₁₀, M=552.52, monoclinic, a=6.6836(2), b=23.4173(6),c=8.3689(2) Å, β=106.174(2)°, V=1257.99(6) Å³, T=100(2) K, space groupP2₁/c, Z=2, ρ=1.46 g·cm⁻³, μ(CU_(Kα))=0.11 mm⁻¹, 3828 independentobserved reflections, 2322 reflections with I>2σ(I), R_(int)=0.097,R[F²>2σ(F²)]=0.051, wR(F²)=0.123.

FIG. 35 is an ORTEP drawing of co-crystal 6α·3β. The hydrogen atoms areomitted for clarity. There is one PMDI β and one napthalene-based α inthe unit cell. All ellipsoids are displayed at the 50% probabilitylevel.

The magnetic properties of LASO co-crystals are characterised by SQUIDmagnetometry (FIG. 39). Magnetic hysteresis is observed at lowtemperature for compounds 1α·9β and 1α·12β. Samples for SQUIDmagnetometry are prepared by packing LASO crystals into a non-magneticgel capsule. Masses for the sample range from 10 mg to 30 mg. Themagnetism as a function of temperature is also measured for bothco-crystals (FIG. 40). Great care is taken during the preparation ofLASO samples to prevent the introduction of magnetic impurities.Compounds 1α, 9β, 10β, and 12β are recrystallised multiple times andstored in a drybox prior to use. No metal instruments or containers areused during the process. Samples for SQUID magnetometry are prepared ina laminar flow hood. ICP-AES is performed by Galbraith Laboratories todirectly address concerns over the possible presence of iron impurities.FIG. 41 are analysis reports of iron content in solvents used for theco-crystallisation of 1α·9β, 1α·10β, and 1α·12β: 1-chlorobutane, 1,2dichloroethane, and diethyl ether. FIG. 44 are analysis reports of ironcontent on co-crystals 1α·9β and 1α·12β. The overall iron content isvery low. The less than symbol (<) indicates that the iron content isbelow the sensitivity limit of the instrument. Iron analysis of bothindependent compounds, simple mixes of D-A molecules, and chargetransfer crystals are also performed. As an example, to illustrate theoverall low iron content in LASO starting materials, compounds 1α and 9βare analyzed (FIG. 42). Compounds 1α and 9β are coarsely mixed togetherto form a charge transfer powder and measured by both SQUID magnetometryand iron analysis (FIG. 43). In FIG. 43, the black is indicative ofcharge transfer and complexation. M(H) curves at 7° K for mixed powderof compound 1α and 9β. No hysteresis is observed, solely diamagneticcontribution from the powder and capsule container. Both graphs are ofthe same sample, with different x-axis scale to illustrate the lack offerromagnetic hysteresis. Iron analysis report for the above mixedcompound powder is provided (bottom image).

The low magnetic saturation signal observed indicates the possibility ofextrinsic magnetisation. To further quantify whether magnetism isderived from LASO networks or a tertiary impurity, low-temperaturemagnetic force microscopy (MFM) is performed.

These MFM measurements are performed at 45° K in two modes: lift-off andz-spectroscopy. In the case of the former, the topography of compound1α·12β is first measured (FIG. 45). A second scan of the same regionwith a magnetised cantilever is performed while approximately 10, 20,30, 50, and 80 nm above the surface. At all heights, topography is stillvisible in the measurement while in phase-locked loop mode (FIG. 45).

The influence of topography is evident in the scan 80 nm above thecrystal surface. Therefore, Z-spectroscopy is performed to ascertainwhether LASO materials are inherently magnetic (FIG. 46). The presenceof both attractive and repulsive interactions with a magnetizedcantilever proves that magnetic domains exist within the material.Though a prominent magnetic hysteresis loop is observed by SQUIDmagnetometry, the lack of a characteristic repulsive force inZ-spectroscopy suggests that LASO networks are not inherently magnetic.

Samples studied by low temperature MFM are also charge compensated at800 mV. Kelvin-probe measurements on the surface of compound 1α·12β showsome differences in charge distribution, possibly due to ferroelectricdomains.

Ferroelectric hysteresis loops are obtained at low temperatures forcompounds 1α·9β, 1α·10β and 1α·12β. Large voltages are needed to achievepolarization saturation (>1 kV). This large voltage results in crystalmelting and dielectric breakdown at higher temperatures. Thus, to obtainhysteresis at room temperature, LASO materials are under-polarized toobtain hysteresis.

LASO materials based on Pyrene demonstrated hysteresis from lowtemperature (7 K, 150 K) upto room temperature (FIG. 47). Compoundsbased on tetrathiafulvalene showed large hysteresis at low temperatureswith nice saturation upto 1.6 kV (FIG. 48). This unexpectedly largepolarization is likely the result of CT processes and proton dynamics.

Challenges with higher temperature and higher voltage measurementsprevent the recording of saturated hysteresis curves. The main issue islikely avalance breakdown and crystal melting at high voltages (>1 kV).Devices that begin with long needles (FIG. 49a ) are destroyed andemerge as re-crystallized solids on the electrode (FIG. 49b ). Crystalnetworks can be formed into ferroelectric devices with gold paste andwire. At high voltages (>900V) and higher temperatures, crystalsfrequently melt likely due to high leakage currents and avalanchebreakdown.

Example 1

1α (Scheme 1): Pyromellitic dianhydride (5.00 g, 22.9 mmol) is added toa 40 mL pressure tube containing 2-(2-aminoethoxy)ethanol (4.7 mL, 46.8mmol). The reaction mixture is heated to 160° C. and stirred for 24hours. After cooling to ambient temperatures, the solid is dissolved intrifluoroacetic acid (100 mL), and the resulting solution is stirred for24 hours. The mixture is then neutralized with a saturated NaHCO₂aqueous solution, and the precipitate is filtered and washed with H₂O(3×100 mL).

The crude product is recrystallized twice from THF and Et₂O to yield asticky white solid (5.49 g, 61%) of 1α. ¹H NMR (500 MHz, CD₃COCD₃, 298K): δ=8.21 (s, 2H), 3.90 (t, J=5.9 Hz, 4H), 3.75 (t, J=5.9 Hz, 4H), 3.55(m, 8H). ¹³C NMR (125 MHz-CD₃COCD₃, 298 K): δ=38.6, 61.9, 67.7, 71.6,119.3, 137.4, 166.9. HR ESI: calcd for [M+H]⁺ m/z=393.1298. foundm/z=393.1299.

Discussion

Using the LASO platform, ten co-crystals are grown (FIG. 2a ) from 12 αsand βs. As the co-crystals grew, three distinguishing features emerged:(i) growth rate, (ii) size, and (iii) morphology. The growth rate iscontrolled by adjusting the total concentration of α and β in thecrystallizing solution, and crystal size can be changed with growthtime. The morphology of the materials (FIG. 2a ) does not change withsubsequent crystallizations. Only one system (1α·7β) is found to containa small amount of polymorphic material. Seven of the co-crystals grew aslong prisms (1α·9β, 1α·10β, 1α·12β, 2α·9β, 2α·11β, 6α·3β, 5α·3β). Thesystem 5α·4β also grew as a prism but assumed a shorter cuboidal shape.Complexes 1α·7β and 1α·8β have the most unusual morphology. Thesematerials grew rapidly in two dimensions, giving them the appearance ofthin sheets.

Using the concentration of α and β (Table 1), the growth time ofhigh-quality single crystals (cm length-scale) is optimized to a periodof several days (FIG. 2a ). The LASO systems 6α·3β and 5α·3β arecrystallized from H₂O/N-methylpyrrolidone and takes 5 days to reach themaximum size. The eight remaining co-crystals finish growing slightlyfaster (3 days) from anhydrous 1-chlorobutane/1,2-dichloroethane/diethylether. Notably, many of the αβ pairs show visible co-crystals ˜2 hoursafter being mixed in the crystallizing solution, indicating the strongdrive for self-assembly. Although LASO materials are capable ofexpedient growth, strict adherence to the optimized solvent conditionsis crucial for successful co-crystallization. FIG. 2b shows theprevalent out-growth of 1α·9β when the crystallizing solution iscontaminated with trace amounts of H₂O, indicating the strong influencesolvent conditions have on the crystal morphology.

FIG. 37 provides images of complex 1α·9β and 1α·10β growing along theglass of the crystallising container. This type of growth indicates thepossibility of controlled growth of LASO on surfaces.

Two co-crystallizations of DA pairs are used as controls in order todemonstrate that arms are crucial to the self-assembly of LASO materials(FIG. 2c ). The first experimental control is the growth of 313.93, aco-crystal with two βs. This co-crystal is equivalent to LASO systems1α·9β and 6α·3β, except it lacks a α′-arm. Without an α′-arm, neithercomponent in 3β·9β can engage in adaptive intermolecular recognition,the phenomenon which is the key attribute in the LASO platform.Co-crystal 3β·9β is grown from diffusion of 1-chlorobutane into1,2-dichloroethane/diethyl ether/N-methylpyrrolidone under anhydrousconditions. For the crystallization, 3β and 9β are used in 1:2 ratio ata concentration of 2 mg/mL of 3β. 3β·9β co-crystals grew as black incolor, similar to the color of both 1α·9β and 6α·3β, yet the crystalsize is significantly smaller and the quality is not adequate forstructure determination by X-ray crystallography (FIG. 2c ). This resultsuggests that the α′-arm, used for adaptive intermolecular recognitionby the as, is crucial for self-assembly in LASO systems.

The second control experiment is to co-crystallize tetrathiafulvalene(TTF) with 1α. A crystal of TTF·12β is the co-crystal equivalent of1α·12β but lacking the β-arms. This control demonstrates that the β-armsare important for crystal growth. Diffusion of 1-chlorobutane into1,2-dichloroethane/diethyl ether is used as the solvent system and,after 14 days at −22° C., only discolored crystals of 1α are found togrow. For the crystallization, 1β and TTF are used in 1:2 ratio at aconcentration of 2 mg/mL of 1β. This result shows that the β-arm is nota passive observer since these appendages also promote theco-crystallization of α and β. From these control experiments, itappears that both the conformationally flexible α′-arm and the rigidβ-arm must be present for self-assembly to occur. These arms appear toenhance the supramolecular affinity between αβ CT pairs and providestability (ΔG of the lattice ground state) to the LASO network solidthrough interstack H-bonding.

FIG. 3 illustrates the use of adaptive intermolecular recognition by anα inside a LASO network solid. In 1α·9β, the flexible α′-arms of 1αadopt two distinct conformations in the lattice (acceptor 1 and acceptor2) to drive the system to an energetically favorable network topology.The arm conformation of the two as mold to adjoining intermolecularrecognition sites. The conformational isomer of a can vary significantly(FIG. 4 and FIG. 5) depending upon the β that is used to generate a LASOnetwork solid. In the local network structure 1α·9β, α′-α and α′-α′H-bonds (FIG. 3) bind neighboring as together, and the α′-β and α-β arminteractions form intermolecular H-bonds between adjacent αs and βs. Theresulting topology is a highly interconnected three-dimensional (3-D)supramolecular network (FIG. 5a ).

The crystal superstructures for all ten LASO materials are elucidatedfrom single-crystal X-ray diffraction data (FIG. 4). Each of the systemshas stacks of alternating donors and acceptors (DADA) and amultidimensional H-bonded network (1D-3D). The space groups of the LASOco-crystals are listed in Table 3. While eight of the systems exhibitthe typical 1-D packing of a mixed stack, two co-crystals are distinctfrom the rest. Systems 1α·7β and 1α·8β (FIG. 2a ), display a previouslyunknown packing motif for CT crystals (FIG. 5). In these systems, theratio of α (acceptor) to β (donor) is 2:1 where the as engage in CT withthe β through π-face-to-π-face (ff) and edge-to-π-face stacking (ef),respectively. As a result of the ff and ef packing, there are two CTaxes (bidirectional CT) in these systems (1α·7β and 1α·8β) thatintersect at an angle of ˜90°. As referred to herein, this packing motifis a “crossed stack”. The resulting arrangement is a checkerboard-pattern of αs and βs which lie parallel to the plane [001].

TABLE 3 Co-Crystal Space Group ρ^(b) 1α · 9β P1 0.68 1α · 10β Pn 0.89 1α· 12β P2₁ 0.43 1α · 7β P1 0.53_(ff), 0.47_(ef) 1α · 8β P1 0.57_(ff),0.42_(ef) 2α · 9β PT 0.58 2α · 11β PT 0.44 6α · 3β P2₁/c 0.27 5α · 3β PT0.45 5α · 4β Pc 0.12

Importantly for self-assembly, the intermolecular H-bonds between thearms establish the pattern of local connectivity for neighboringmolecules. It is the global topology, however, of the H-bonded networkthat is a primary distinguishing feature of a LASO co-crystal. In FIG.5, a noncovalent connectivity diagram (Etter, M. C. Acc. Chem. Res.1990, 23, 120-126; Etter, M. C., et al. Acta Crystallogr., Sect. B:Struct. Sci 1990, 46, 256-262; Bernstein, J., et al. Angew. Chem. Int.Ed. 1995, 34, 1555-1573; Motherwell, W. D. S., et al. Acta Crystallogr.,Sect. B: Struct. Sci 1999, 55, 1044-1056; Grell, J., et al. ActaCrystallogr., Sect. B: Struct. Sci 1999, 55, 1030-1043; Grell, J., etal. Acta Crystallogr., Sect. B: Struct. Sci 2000, 56, 166-166, allincorporated herein by reference) for three systems (1α·9β, 1α·10β,1α·12β) is used to illustrate the diverse global topology of theH-bonded network in a LASO platform. This structural feature ispartially ascribed to the ability of 1α to engage in adaptiveintermolecular recognition. By varying the identity of β in these threeco-crystals, the binding conformation of 1α (inset of FIG. 5) along withthe network topology changes. FIG. 5 shows that topologically, theH-bonding in 1α·9β can be represented by a single 3-D network (FIG. 5a). By contrast, co-crystals 1α·10β and 1α·12β each consist ofinterpenetrating network topologies. The former is found to be fashionedfrom a pair of distinct 3-D networks (FIG. 5b ), and the latter can berepresented as a 3-D network entwined with a series of repeating 2-Dnetworks, respectively.

In addition to the structural characteristics, the choice of thecorresponding DA pairs (αβ) has a significant effect on the value of ρ(ionicity) for each system (Eddaoudi, M., et al. Acc. Chem. Res. 2001,34, 319-330, incorporated herein by reference). In Table 3, β for theten LASO co-crystals is shown to vary ρ=0.12-0.89, another result thathighlights the modularity of LASO network solids. Three of the systemscan be classified as ionic (1α·9β, 1α·10β, 2α·9β), five co-crystals aremixed valent (1α·7β, 1α·8β, 1α·12β, 2α·11β, 5α·3β), and the remainingtwo materials are neutral (5α·4β, 6α·3β). For convenience, the crossedstack systems 1α·7β and 1α·8β are grouped into the mixed valencecategory. The two crossing stacks (ff and ef) are found, however, tohave different values for ρ (Table 3). This dichotomy makes the crossedstack systems a mixed valent/neutral hybrid co-crystal. Four of theeight mixed stack systems (1_(α)·9_(β), 1_(α)·10_(β), 1_(α)·12_(β),5_(α)·3_(β)) display the spectroscopic signature of an asymmetriclattice caused by the dimerization of donors and acceptors. Inone-dimensional CT systems, this phenomenon is the result of quantuminstabilities, e.g., the Peierls (Torrance, J. B., et al. Phys. Rev.Lett. 1981, 46, 253-257; Torrance, J. B., et al. Phys. Rev. Lett. 1981,47, 1747-1750; Iwasa, Y., et al. Phys. Rev. B: Condens. Matter 1990, 42,2374-2377; Bruinsma, R., et al. Phys. Rev. B: Condens. Matter 1983, 27,456-466; Girlando, A., et al. J. Chem. Phys. 1983, 79, 1075-1085;Masino, M., et al. Phys. Chem. Chem. Phys. 2001, 3, 1904-1910; Horiuchi,S., et al. Science 2003, 299, 229-232; Tokura, Y., et al. Solid StateCommun. 1986, 57, 607-610; Girlando, A., et al. Solid State Commun.1986, 57, 891-896; Collet, E., et al. Science 2003, 300, 612-615;Koshihara, S., et al. Phys. Rev. B: Condens. Matter 1990, 42, 6853-6856;Mitani, T., et al. Phys. Rev. Lett. 1984, 53, 842-845; Tokura, Y., etal. Phys. Rev. B: Condens. Matter 1988, 38, 2215-2218; and Iwasa, Y., etal. Phys. Rev. B: Condens. Matter 1989, 39, 10441-10444, allincorporated herein by reference) and Spin-Peierls transitions(Girlando, A., et al. Solid State Commun. 1985, 54, 753-759; Hughes, R.C., et al. J. Chem. Phys. 1968, 48, 1066-1076; Huizinga, S., et al.Phys. Rev. B: Condens. Matter 1979, 19, 4723-4732; Hasegawa, T., et al.Solid State Commun. 1997, 103, 489-493; Kagawa, F., et al. Nature Phys.2010, 6, 169-172, all incorporated herein by reference).

Several LASO materials are found to contain structural disorder in thelattice. Systems 1α·8β and 2α·11β both contain asymmetric βs thatexhibit substitutional disorder. In 2α·9β, the α′-arm of 2α and thearomatic ring system of 9β are found to have positional disorder. Thelack of long-range periodicity has a noticeable effect on theself-assembly since 15 equivalents of 9β (Table 1) are needed in thecrystallizing solution before co-crystals begin to grow.

The redox potentials of the first electron transfer processes of theindividual species 1α,9β,10β and 12β are recorded in DMF at 298° K usingboth CV and SWDPV (Table 4). In the case of an irreversible oxidationprocess for compounds 9β and 10β, the redox potential determined by CVis estimated, assuming a one-electron process based on the expectedseparation between anodic and cathodic peaks for a Nernstian process.

TABLE 4 Compound CV^(a)/V C SWDPV^(a)/V 1α^(b) −0.73 −0.73 9β^(c)+0.80^(d) +0.82 10β^(c) +0.83^(d) +0.81 12β^(c) +0.40 +0.40^(a)Collected at 298° K in argon-purged DMF ^(b)First reduction process^(c)First oxidation process ^(d)Irreversible process, estimated assuminga one-eletron process

The LASO platform presented herein is a type of molecular recognitionthat can amplify the growth of donor and acceptor co-crystals (cmlength-scale) under ambient conditions in 3-5 days. The LASO strategyhas three components which work cooperatively to promote growth of thenetwork solid. The main constituent is a donor/acceptor (α-complement)that uses flexible appendages (diethylene glycol, α′-arm) to formintermolecular H-bonds in the crystal. The second constituent is asmaller CT partner (β-complement) with short and relatively rigidH-bonding functionalities (C═O, —NH₂, —OH, β-arm) that is incorporatedinto the LASO network through molecular recognition with theα-complement. The final element is the solvent system that promotes theco-crystallization of the α-complement and β-complement. With thisplatform, supramolecular architectures combine the H-bonded network andstacks of alternating donors and acceptors. Not only does the LASOstrategy produce network solids that are capable of amplified co-crystalgrowth, but it creates an entirely new 2-D donor and acceptor packingmotif made of two perpendicular CT axes, i.e., the crossed stack.

As further described herein, a molecular design that allows donor andacceptor molecules to self-assemble into CT ferroelectric networks atambient temperatures is afforded. The co-crystals solve thelong-standing challenge that DA mixed stack materials can exhibit aferroelectric T_(c) above room temperature. The demonstration offerroelectric properties in an organic network enables new opportunitiesto produce these systems into new forms with exciting function such aselectrically addressable hydrogels, ferroelectric catalysts, andCT-based sensitizers for photovoltaics, among others. The combination ofdonor-acceptor interactions with hydrogen bonded networks offers apromising supramolecular platform to design novel organic electronicstructures.

The disclosures of all articles and references, including patents, areincorporated herein by reference. The invention and the manner andprocess of making and using it are now described in such full, clear,concise and exact terms as to enable any person skilled in the art towhich it pertains, to make and use the same. All references cited inthis specification are incorporated herein by reference. It is to beunderstood that the foregoing describes preferred embodiments of thepresent invention and that modifications may be made therein withoutdeparting from the spirit or scope of the present invention.

What is claimed is:
 1. An organic charge-transfer (CT) co-crystalconsisting essentially of an electron acceptor molecule (A) and anelectron donor molecule (D), wherein one of A and D is an α-complementand the other one of A and D is a β-complement, such that theβ-complement is incorporated into the α-complement through molecularlinkages in a solvent system to form a co-crystalline supramolecularnetwork, wherein one or more of the molecular linkages between theα-complement and the β-complement use adaptive intermolecularrecognition to form the one or more molecular linkages, the co-crystalcharacterized by having a crystal superstructure comprising a mixedstack lattice (DADADA) and a topological hydrogen-bonded network.
 2. Anorganic CT co-crystal according to claim 1, wherein A is a diimide. 3.An organic CT co-crystal according to claim 2, wherein A is selectedfrom the group consisting of 1α,2α,3β and 4β; and D is selected from thegroup consisting of 5α, 6α; 7β, 8β, 9β, 10β, 11β and 12β.
 4. An organicCT co-crystal according to claim 1, wherein the solvent system is one ormore organic solvents.
 5. An organic CT co-crystal according to claim 4,wherein the solvent system is selected from the group consisting ofdichloroethane/diethyl ether and N-methylpyrrolidone.
 6. An organic CTco-crystal according to claim 1, wherein the α-complement has an α′-armthat is a diethylene glycol moiety.
 7. An organic CT co-crystalaccording to claim 1, wherein the hydrogen-bonded network comprisesinterstack and intrastack hydrogen bonds.
 8. An organic CT co-crystalaccording to claim 1, wherein the co-crystal is devoid or substantiallydevoid of solvent.
 9. An organic CT co-crystal according to claim 1,wherein the α-complement has an α′-arm that has one or morehydrogen-bonding recognition sites.
 10. An organic CT co-crystalaccording to claim 9, wherein the one or more hydrogen-bondingrecognition sites is independently selected from the group consisting ofamino, carbonyl, ether and hydroxyl moieties.
 11. An organic CTco-crystal according to claim 1, wherein the A has at least four arms,of which at least one is an α′-arm.
 12. An organic CT co-crystalaccording to claim 11, wherein the B has at least one arm.
 13. Anorganic CT co-crystal according to claim 1, wherein the co-crystal isgrown in the dark, under ambient conditions.
 14. An organic CTco-crystal according to claim 13, wherein the co-crystal is grown usingliquid diffusion.
 15. An organic CT co-crystal according to claim 3selected from the group consisting of 1α·7β, 1α·8β, 1α·9β, 1α·10β,1α·12β, 2α·9β, 2α·11β, 6α·3β, 5α·3β and 5α·4β.
 16. An organic CTco-crystal according to claim 1, wherein the co-crystal has a packingmotif that is a crossed stack.